1. Field of the Invention
The present invention relates to a process for producing tyres for vehicle wheels.
In particular, the present invention relates to a process for producing tyres built on a toroidal support.
Another object of the invention is a plant for producing tyres for vehicle wheels, able to be used to carry out the aforementioned producing process.
2. Description of the Related Art
The production cycles of a tyre provide that, after a building process in which the various components of the same tyre are made and/or assembled in a building line, a vulcanization and moulding process is carried out, in a suitable vulcanization line, adapted for defining the structure of the tyre according to a desired geometry and tread pattern.
A tyre generally comprises a toroidally ring-shaped carcass including one or more carcass plies, strengthened with reinforcing cords, lying in substantially radial planes, (a radial plane contains the rotation axis of the tyre). Each carcass ply has its ends integrally associated with at least one metal reinforcing annular structure, usually known as bead core, constituting the reinforcing at the beads, i.e. at the radially internal ends of the tyre, the function of which is to enable assembling of the tyre with a corresponding mounting rim. Placed crown wise to said carcass is a band of elastomer material, called tread band, in which, at the end of the vulcanization and molding steps, a raised pattern is formed for ground contact. A reinforcing structure usually known as belt structure is placed between the carcass and the tread band. In the case of car tyres, this structure usually comprises at least two radially superposed strips of rubberised fabric provided with reinforcing cords, generally of metal material, positioned parallel to each other in each strip and in a crossed relationship with the cords of the adjacent strip preferably symmetrically arranged with respect to the equatorial plane of the tyre. Preferably said belt structure further comprises at a radially external position thereof, at least on the ends of the underlying belt strips, also a third layer of textile or metallic cords, circumferentially disposed (at zero degrees).
Finally, in tyres of the tubeless type, i.e. devoid of an air tube, a radially internal layer, called liner, is present which has imperviousness features to ensure the air-tightness of the tyre.
To the aims of the present description as well as in the following claims, by the term “elastomer material” it is intended a composition comprising at least one elastomer polymer and at least one reinforcing filler. Preferably this composition further comprises additives such as cross-linking and/or plasticizing agents. By virtue of the cross-linking agents, this material can be cross-linked through heating so as to form the final manufactured article.
In recent times tyre production processes in which a green tyre is built on a rigid toroidal support has been introduced in the field. Said processes are preferably used for tyres produced starting from a limited number of elementary semifinished products fed onto a toroidal support whose outer profile coincides with that of the radially internal surface of the tyre that is wished to be produced. The toroidal support is moved, preferably by means of a robotized system, among a plurality of working stations in each of which, through automated sequences, a particular building step of the tyre is carried out. At the end of the building steps, the toroidal support with the tyre supported thereby is arranged inside a vulcanization mould.
In the present context, by the term “green tyre” a tyre obtained by the building process is indicated.
An example of the aforementioned processes is described in WO 01/32409, in the name of the same Applicant, which illustrates a tyre building line provided with working stations, each arranged to make and assemble at least one structural component of the tyre being processed, in which at least one series of tyres comprising at least a first and a second tyre model that are different from each other is treated simultaneously, and in which the transferral of the tyres to the vulcanization line is carried out through robotized arms and according to a transferring rate which is equal to the transferring rate of the tyres to each of said working stations.
WO 01/39963, in the name of the same Applicant, on the other hand, illustrates a process for producing tyres that are different from each other, comprising a building unit having a plurality of working stations, each adapted for assembling at least one structural component on at least one type of tyre being processed, a vulcanization unit, and a device for transferring and moving the tyre being processed, operating between the working stations and the vulcanization unit.
Said device for transferring and moving the tyre transfers a green tyre to the vulcanization unit; after vulcanization, it picks up a vulcanized and moulded tyre from the vulcanization unit and transfers it to the first working station of the building unit, where the tyre is removed from the corresponding toroidal support. The latter is then transferred from the same device for transferring and moving the tyre into a temperature stabilizing device. In the case in which the tyre to be produced requires a different type of toroidal support, the device picks up the suitable toroidal support from a feeding station and inserts it into the temperature stabilizing device.
The Applicant has noted that since the aforementioned device for transferring and moving the tyre is arranged to carry out numerous operations and to make large displacements, requires large maneuvering spaces and therefore a plant of considerable size. In particular WO 01/39963 describes the use of a robotized arm translating on a rail, as a device for transferring and moving the tyre.
The Applicant has also verified that, in such known processes, any anomaly or malfunctioning in any one from the vulcanization unit, mounting/dismounting unit of the toroidal supports, and temperature stabilizing unit, has the immediate consequence of blocking the production plant with serious repercussions on its productivity.
For example, in the case of blocking of the mounting/dismounting unit of the toroidal support, the device for transferring and moving the tyre does not carry out the removal of the tyre from the vulcanizer, even if the vulcanization has been completed. Consequently, the tyre obtained becomes overvulcanized and therefore is not in accordance with the required specifications.